Ceramics comprising Al2O3, Y2O3, ZrO2 and/or HfO2, and Nb2O5 and/or Ta2O5 and methods of making the same

ABSTRACT

Ceramics comprising (i) at least one of Nb 2 O 5  or Ta 2 O 5  and (ii) at least two of (a) Al 2 O 3 , (b) Y 2 O 3 , or (c) at least one of ZrO 2  or HfO 2 . Embodiments of ceramics according to the present invention can be made, formed as, or converted into optical waveguides, glass beads, articles (e.g., plates), fibers, particles (e.g., abrasive particles), and thin coatings.

This application is a divisional of U.S. Ser. No. 10/666,098, filed Sep.18, 2003, now allowed, the disclosure of which is incorporated byreference in its entirety herein.

BACKGROUND

A number of amorphous (including glass) and glass-ceramic compositionsare known. Many oxide glass systems utilize well-known glass-formerssuch as SiO₂, B₂O₃, P₂O₅, GeO₂, TeO₂, As₂O₃, and V₂O₅ to aid in theformation of the glass. Some of the glasses can be heat-treated to formglass ceramics.

SUMMARY

In one aspect, the present invention provides glasses and glass-ceramicscomprising (i) at least one of Nb₂O₅ or Ta₂O₅ and (ii) at least two of(a) Al₂O₃, (b) Y₂O₃, or (c) at least one of ZrO₂ or HfO₂. In someembodiments, the glass is present in a ceramic (i.e., ceramic comprisingthe glass). Optionally, embodiments of glass according to the presentinvention can be heat-treated to convert at least a portion of the glassto crystalline ceramic to provide a glass-ceramic.

Embodiments of glasses according to the present invention may be useful,for example, for optical applications (e.g., lenses, optical coatings,retroreflective elements, windows (e.g., infrared (IR) windows), andoptical waveguides). Some embodiments of glasses according to thepresent invention (e.g., those utilized in optical waveguides) may beused as a host material for the rare earth dopants, wherein if a “rareearth dopant” and an “REO” are both present in the glass, the rare earthdopant and REO are different.

In some embodiments, the present invention provides glass collectivelycomprising at least 70 (in some embodiments, at least 75, 80, 85, 90,95, 97, 98, 99, or even 100) percent by weight of (i) at least one ofNb2O₅ or Ta₂O₅ and (ii) at least two of (a) Al₂O₃, (b) Y₂O₃, or (c) atleast one of ZrO₂ or HfO₂, and containing not more than 30 (in someembodiments, not more than 25, 20, 15, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1,0.5, 0.1, or even zero) percent by weight collectively As₂O₃, B₂O₃,GeO₂, P₂O₅, SiO₂, TeO₂, and V₂O₅, based on the total weight of theglass. In some embodiments, the glass comprises at least 1, 2, 3, 4, 5,10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, or even at least 70percent by weight Al₂O₃, at least 1, 2, 3, 4, 5, 10, 15, 20, 25, 30, 35,40, 45, 50, 55, 60, 65, or even at least 70 percent by weight Y₂O₃; atleast 1, 2, 3, 4, 5, 10, 15, 20, 25, 30, or even at least 35 percent byweight ZrO₂ (in some embodiments, ZrO₂ and/or (including collectively)HfO₂); and/or at least 1, 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 45,50, 55, 60, 65, or even at least 70 percent by weight of at least one ofNb₂O₅ or Ta₂O₅, based on the total weight of the glass. In someembodiments, the glass comprises at least 1 (in some embodiments, atleast 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55,60, 65, 70, 75, or even at least 80) percent by weight of the at leastone of Nb₂O₅ or Ta₂O₅, based on the total weight of the glass. In someembodiments, the present invention provides a ceramic comprising theglass (in some embodiments, at least 1, 2, 3, 4, 5, 10, 15, 20, 25 30,35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 96, 97, 98, 99, oreven 100 percent by volume of the glass).

In some embodiments, the present invention provides a glass-ceramiccollectively comprising at least 70 (in some embodiments, at least 75,80, 85, 90, 95, 97, 98, 99, or even 100) percent by weight (i) at leastone of Nb₂O₅ or Ta₂O₅ and (ii) at least two of (a) Al₂O₃, (b) Y₂O₃, or(c) at least one of ZrO₂ or HfO₂, and containing not more than 30 (insome embodiments, not more than 25, 20, 15, 10, 9, 8, 7, 6, 5, 4, 3, 2,1, 0.5, 0.1, or even zero) percent by weight collectively As₂O₃, B₂O₃,GeO₂, P₂O₅, SiO₂, TeO₂, and V₂O₅, based on the total weight of theglass-ceramic. In some embodiments, the glass-ceramic comprises at least1, 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, or evenat least 70 percent by weight Al₂O₃, at least 1, 2, 3, 4, 5, 10, 15, 20,25, 30, 35, 40, 45, 50, 55, 60, 65, or even at least 70 percent byweight Y₂O₃; at least 1, 2, 3, 4, 5, 10, 15, 20, 25, 30, or even atleast 35 percent by weight at least one of ZrO₂ or HfO₂; and/or at least1, 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, or evenat least 70 percent by weight of at least one of Nb₂O₅ or Ta₂O₅, basedon the total weight of the glass-ceramic. In some embodiments, theglass-ceramic comprises at least 1 (in some embodiments, at least 2, 3,4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70,75, or even at least 80) percent by weight of the at least one of Nb₂O₅or Ta₂O₅, based on the total weight of the glass-ceramic.

For some embodiments, glasses, glass-ceramics, and crystalline ceramicsaccording to the present invention further comprise at least oneadditional metal oxide (e.g., Y₂O₃, MgO, TiO₂, Cr₂O₃, CuO, SrO, Li₂O,NiO, and/or Fe₂O₃). For some embodiments, glasses, glass-ceramics, andcrystalline ceramics according to the present invention, contain notmore than 20 (in some embodiments, less than 15, 10, 5, 4, 3, 2, 1, 0.5,0.1, or even zero) percent by weight SiO₂ and not more than 20 (in someembodiments, not more than 15, 10, 5, 4, 3, 2, 1, 0.5, 0.1, or evenzero) percent by weight B₂O₃, based on the total weight of the glass,glass-ceramic, and crystalline ceramic, respectively.

Some embodiments of glass-ceramics according to the present inventionmay comprise the glass of the glass-ceramic in an amount, for example,of at least 1, 2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65,70, 75, 80, 85, 90, or even 95 percent by volume, based on the totalvolume of the glass-ceramic. Some embodiments of glass-ceramicsaccording to the present invention may comprise the crystalline ceramicof the glass-ceramic in an amount, for example, of at least 5, 10, 15,20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 98,99, or even 100 percent by volume, based on the total volume of theglass-ceramic.

In some embodiments, the present invention provides a method for makingglass according to the present invention, the method comprising:

-   -   melting sources of (i) at least one of Nb₂O₅ or Ta₂O₅ and (ii)        at least two of (a) Al₂O₃, (b) Y₂O₃, or (c) at least one of ZrO₂        or HfO₂ to provide a melt; and    -   cooling the melt to provide the glass. In some embodiments, the        glass is present in a ceramic (i.e., ceramic comprising the        glass). In some embodiments, the glass can be heat-treated to        convert at least a portion of the glass to crystalline ceramic        to provide a glass-ceramic.

In some embodiments, the present invention provides a method for makingan article comprising glass according to the present invention, themethod comprising:

-   -   providing glass beads comprising glass according to the present        invention (e.g., melting at least sources of (i) at least one of        Nb₂O₅ or Ta₂O₅ and (ii) at least two of (a) Al₂O₃, (b) Y₂O₃,        or (c) at least one of ZrO₂ or HfO₂, as applicable, to provide a        melt;        cooling the melt to provide the glass beads), wherein the glass        has a T_(g); and    -   heating the glass beads above the T_(g) such that the glass        beads coalesce to form a shape and provide the article. In some        embodiments, the glass present in the article can be        heat-treated to convert at least a portion of the glass to        crystalline ceramic to provide a glass-ceramic.

In some embodiments, the present invention provides a method for makingan article comprising glass according to the present invention, themethod comprising:

-   -   providing glass beads comprising glass according to the present        invention (e.g., melting at least sources of (i) at least one of        Nb₂O₅ or Ta₂O₅ and (ii) at least two of (a) Al₂O₃, (b) Y₂O₃,        or (c) at least one of ZrO₂ or HfO₂, as applicable, to provide a        melt;        cooling the melt to provide the glass beads), wherein the glass        has a T_(g); and    -   heating the glass beads above the T_(g) such that the glass        beads coalesce to form a shape and provide the article. In some        embodiments, the glass present in the article can be        heat-treated to convert at least a portion of the glass to        crystalline ceramic to provide a glass-ceramic.

In some embodiments, the present invention provides a method for makingan article comprising glass according to the present invention, themethod comprising:

-   -   providing glass powder comprising glass according to the present        invention (e.g., converting glass beads according to the present        invention to provide the glass powder), wherein the glass has a        T_(g); and    -   heating the glass powder above the T_(g) such that the glass        powder coalesces to form a shape and provide the article. In        some embodiments, the glass present in the article can be        heat-treated to convert at least a portion of the glass to        crystalline ceramic to provide a glass-ceramic. Optionally, the        glass powder is provided by converting (e.g., crushing) glass        (e.g., glass beads and/or bulk glass) according to the present        invention to glass powder.

In some embodiments, glass-ceramic according to the present invention isconverted (e.g., crushed) to provide particles (e.g., abrasiveparticles).

In this application:

“amorphous material” refers to material derived from a melt and/or avapor phase that lacks any long range crystal structure as determined byX-ray diffraction and/or has an exothermic peak corresponding to thecrystallization of the amorphous material as determined by a DTA(differential thermal analysis) as determined by the test describedherein entitled “Differential Thermal Analysis”;

“ceramic” includes glass, crystalline ceramic, glass-ceramic, andcombinations thereof;

“complex metal oxide” refers to a metal oxide comprising two or moredifferent metal elements and oxygen (e.g., CeAl₁₁O₁₈, Dy₃Al₅O₁₂,MgAl₂O₄, and Y₃Al₅O₁₂);

“complex Al₂O₃.metal oxide” refers to a complex metal oxide comprising,on a theoretical oxide basis, Al₂O₃ and one or more metal elements otherthan Al (e.g., CeAl₁₁O₁₈, Dy₃Al₅O₁₂, MgAl₂O₄, and Y₃Al₅O₁₂);

“complex Al₂O₃.Y₂O₃” refers to a complex metal oxide comprising, on atheoretical oxide basis, Al₂O₃ and Y₂O₃ (e.g., Y₃Al₅O₁₂);

“complex Al₂O₃.REO” refers to a complex metal oxide comprising, on atheoretical oxide basis, Al₂O₃ and rare earth oxide (e.g., CeAl₁₁O₁₈ andDy₃Al₅O₁₂);

“glass” refers to amorphous material exhibiting a glass transitiontemperature;

“glass-ceramic” refers to ceramic comprising crystals formed byheat-treating glass;

“T_(g)” refers to the glass transition temperature as determined by thetest described herein entitled “Differential Thermal Analysis”;

“T_(x)” refers to the crystallization temperature as determined by thetest described herein entitled “Differential Thermal Analysis”;

“rare earth oxides” refers to cerium oxide (e.g., CeO₂), dysprosiumoxide (e.g., Dy₂O₃), erbium oxide (e.g., Er₂O₃), europium oxide (e.g.,Eu₂O₃), gadolinium oxide (e.g., Gd₂O₃), holmium oxide (e.g., Ho₂O₃),lanthanum oxide (e.g., La₂O₃), lutetium oxide (e.g., Lu₂O₃), neodymiumoxide (e.g., Nd₂O₃), praseodymium oxide (e.g., Pr₆O₁₁), samarium oxide(e.g., Sm₂O₃), terbium oxide (e.g., Tb₂O₃), thorium oxide (e.g., Th₄O₇),thulium oxide (e.g., Tm₂O₃), and ytterbium oxide (e.g., Yb₂O₃), andcombinations thereof;

“REO” refers to rare earth oxide(s); and

“rare earth dopant” refers to a dopant (i.e., cerium, praseodymium,neodymium, promethium, samarium, europium, gadolinium, terbium,dysprosium, holmium, erbium, thulium, ytterbium, or their othercompounds, and mixtures thereof) that provides light emission inresponse to excitation of its electrons and is a different material thanREO.

Further, it is understood herein that unless it is stated that a metaloxide (e.g., Al₂O₃, complex Al₂O₃.metal oxide, etc.) is crystalline, forexample, in a glass-ceramic, it may be crystalline, or portions glassand portions crystalline. For example, if a glass ceramic comprisesAl₂O₃ and ZrO₂, the Al₂O₃ and ZrO₂ may each be in a glass state,crystalline state, or portions in a glass state and portions in acrystalline state, or even as a reaction product with another metaloxide(s) (e.g., unless it is stated that, for example, Al₂O₃ is presentas crystalline Al₂O₃ or a specific crystalline phase of Al₂O₃ (e.g.,alpha Al₂O₃), it may be present as crystalline Al₂O₃ and/or as part ofone or more crystalline complex Al₂O₃.metal oxides).

Some embodiments of ceramics (e.g., glasses and glass-ceramics)according to the present invention can be made, formed as, or convertedinto beads (e.g., beads having diameters of at least 1 micrometers, 5micrometers, 10 micrometers, 25 micrometers, 50 micrometers, 100micrometers, 150 micrometers, 250 micrometers, 500 micrometers, 750micrometers, 1 mm, 5 mm, or even at least 10 mm), articles (e.g.,plates), fibers, particles, and coatings (e.g., thin coatings).Embodiments of the beads can be useful, for example, in reflectivedevices such as retro-reflective sheeting, alphanumeric plates, andpavement markings. Embodiments of the particles and fibers are useful,for example, as thermal insulation, filler, or reinforcing material incomposites (e.g., ceramic, metal, or polymeric matrix composites).Embodiments of the thin coatings can be useful, for example, asprotective coatings in applications involving wear, as well as forthermal management. Examples of articles according of the presentinvention include kitchenware (e.g., plates), dental brackets, andreinforcing fibers, cutting tool inserts, abrasive materials, andstructural components of gas engines, (e.g., valves and bearings).Exemplary embodiments of other articles include those having aprotective coating of glass-ceramic on the outer surface of a body orother substrate. Certain glass-ceramic particles made according to thepresent invention can be particularly useful as abrasive particles. Theabrasive particles can be incorporated into an abrasive article, or usedin loose form.

In one aspect, the present invention provides an optical waveguidecomprising a substrate (e.g., at least one of silicon or SiO₂); and aglass according to the present invention doped with a rare earth dopanton a surface of the substrate. In some embodiments, the substrate is alower low refractive index layer and further comprises an upper lowrefractive index layer.

In one aspect, the present invention provides an optical waveguidecomprising a glass fiber having a core material and a claddingsurrounding the core material, wherein the core material comprises aglass according to the present invention doped with a rare earth dopant.

In one aspect, the present invention provides an optical amplifiercomprising an optical pump source which provides optical pump light; andan optical waveguide coupled to receive the optical pump light from theoptical pump source, wherein the optical waveguide comprises a glassaccording to the present invention doped with a rare earth dopant.

In one aspect, the present invention provides a method for amplifyingoptical signals, the method comprising:

inputting the optical signals to an optical waveguide comprising a glassaccording to the present invention doped with a rare earth dopant; and

applying pump light to the optical waveguide to cause the waveguide toprovide optical gain to the optical input signals.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a cross-sectional illustration of an exemplary embodiment ofan optical waveguide described herein.

FIG. 2 is a cross-sectional illustration of another exemplary embodimentof an optical waveguide described herein.

FIG. 3 is a cross-sectional illustration of another exemplary embodimentof an optical waveguide described herein.

FIG. 4 is a cross-sectional illustration of another exemplary embodimentof an optical waveguide described herein.

FIG. 5 is a cross-sectional illustration of another exemplary embodimentof an optical waveguide described herein.

FIG. 6 is a cross-sectional illustration of another exemplary embodimentof an optical waveguide described herein.

FIG. 7 is an illustration of an exemplary embodiment of an opticalwaveguide amplifier configuration of the invention.

FIGS. 8 and 9 are scanning electron microscope (SEM) digitalphotomicrographs of Example 15 and 16 materials, respectively.

DETAILED DESCRIPTION

Embodiments of glasses according to the present invention are useful foroptical waveguide applications. Referring to FIG. 1, a cross-sectionalview of an exemplary optical waveguide 10 in accordance with oneexemplary embodiment of the invention is shown. Optical waveguide 10 isshown deposited on a silicon substrate 12 and includes rare earth dopedlayer 14. Rare earth doped layer 14 is sandwiched between two claddinglayers, a lower low refraction index layer 16 and an upper lowrefraction index layer 18. The optical waveguide in FIG. 1 is meant tobe for illustrative purposes only. The glasses described herein may beused in any waveguide configuration that utilizes doped-materials.

Optical waveguides of the invention may also include configurationsknown as “channel” waveguides, “ridge” waveguides, “strip-loaded”waveguides, and “diffused” or “ion exchanged” waveguides and waveguidesin the form of a fiber. FIGS. 2-6 show illustrations of cross-sectionsof such embodiments depicted as waveguides 100, 200, 300, 400, and 500.Referring to FIGS. 2-4, rare earth doped glass 102, 202, 302, 402 isadjacent to a lower low refractive index layer deposited on a siliconsubstrate 104, 204, 304, 404. Upper low refractive index layer 206, 306is in contact with rare earth doped glass 202, 302 in some embodiments.Referring to FIG. 6, rare earth doped glass core 502 is surrounded bylow refractive index cladding 504. Examples of useful low refractiveindex materials for use in the optical waveguides of the inventioninclude SiO₂, SiON, and glasses (un-doped) comprising for example,lanthanum, aluminum, and/or zirconium oxide. In some instances, it maybe desirable to use an un-doped glass as described below, as the glassof an optical waveguide.

FIG. 7 illustrates an exemplary standard waveguide amplifierconfiguration 20 containing an optical waveguide 22. Optical signals areinput into the optical waveguide 22 via an optical isolator 24 and awaveguide division multiplexing (WDM) coupler 26. An optical pump signalfrom an optical pump source 28 is also input into the optical waveguide22 via the WDM coupler 26. The amplified output signals from the opticalwaveguide 22 are output through a second optical isolator 30. Theoptical isolators 22, 30 are included to eliminate backward reflectionsfrom the optical waveguide 22 to the input port and from the outputport, respectively. The above waveguide amplifier configuration is forillustrative purposes only. More detailed information regardingwaveguide amplifiers may be found in U.S. Pat. No. 6,490,081 B1(Feillens et al). The optical waveguides of the invention may be usefulin any configuration used to amplify optical signals.

Ceramics (including glasses and glass-ceramics) according to the presentinvention can be prepared by selecting the raw materials, the desiredcomposition, and the processing technique(s).

Sources, including commercial sources, of (on a theoretical oxide basis)Al₂O₃ include bauxite (including both natural occurring bauxite andsynthetically produced bauxite), calcined bauxite, hydrated aluminas(e.g., boehinite, and gibbsite), aluminum, Bayer process alumina,aluminum ore, gamma alumina, alpha alumina, aluminum salts, aluminumnitrates, and combinations thereof. The Al₂O₃ source may contain, oronly provide, Al₂O₃. Alternatively, the Al₂O₃ source may contain, orprovide Al₂O₃, as well as one or more metal oxides other than Al₂O₃(including materials of or containing complex Al₂O₃ metal oxides (e.g.,Dy₃Al₅O₁₂, Y₃Al₅O₁₂, CeAl₁₁O₁₈, etc.)).

Sources, including commercial sources, of Nb₂O₅ include niobium oxidepowders, niobium containing ores (e.g., columbite, tantalite, andeuxelite), niobium salts, niobium metals, and combinations thereof.

Sources, including commercial sources, of Ta₂O₅ include tantalum oxidepowders, tantalum containing ores (e.g., columbite, tantalite, andeuxelite), tantalum salts, tantalum metals, and combinations thereof.

Sources, including commercial sources, of (on a theoretical oxide basis)Y₂O₃ include yttrium oxide powders, yttrium, yttrium-containing ores,and yttrium salts (e.g., yttrium carbonates, nitrates, chlorides,hydroxides, and combinations thereof). The Y₂O₃ source may contain, oronly provide, Y₂O₃. Alternatively, the Y₂O₃ source may contain, orprovide Y₂O₃, as well as one or more metal oxides other than Y₂O₃(including materials of or containing complex Y₂03.metal oxides (e.g.,Y₃Al₅O₁₂)).

Sources, including commercial sources, of (on a theoretical oxide basis)ZrO₂ include zirconium oxide powders, zircon sand, zirconium,zirconium-containing ores, and zirconium salts (e.g., zirconiumcarbonates, acetates, nitrates, chlorides, hydroxides, and combinationsthereof). In addition, or alternatively, the ZrO₂ source may contain, orprovide ZrO₂, as well as other metal oxides such as hafnia. Sources,including commercial sources, of (on a theoretical oxide basis) HfO₂include hafnium oxide powders, hafnium, hafnium-containing ores, andhafnium salts. In addition, or alternatively, the HfO₂ source maycontain, or provide HfO₂, as well as other metal oxides such as ZrO₂.

For embodiments comprising ZrO₂ and HfO₂, the weight ratio of ZrO₂:HfO₂may be in a range of 1: zero (i.e., all ZrO₂; no HfO₂) to zero: 1, aswell as, for example, at least about 99, 98, 97, 96, 95, 90, 85, 80, 75,70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, and 5 parts (byweight) ZrO₂ and a corresponding amount of HfO₂ (e.g., at least about 99parts (by weight) ZrO₂ and not greater than about 1 part HfO₂) and atleast about 99, 98, 97, 96, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45,40, 35, 30, 25, 20, 15, 10, and 5 parts HfO₂ and a corresponding amountof ZrO₂.

Other useful metal oxides may also include, on a theoretical oxidebasis, BaO, CaO, Cr₂O₃, CoO, Fe₂O₃, GeO₂, Li₂O, MgO, MnO, NiO, Na₂O,REO, Sc₂O₃, SrO, TiO₂, ZnO, and combinations thereof. Sources, includingcommercial sources, include the oxides themselves, metal powders,complex oxides, ores, carbonates, acetates, nitrates, chlorides,hydroxides, etc. For example, sources, including commercial sources, ofrare earth oxides include rare earth oxide powders, rare earth metals,rare earth-containing ores (e.g., bastnasite and monazite), rare earthsalts, rare earth nitrates, and rare earth carbonates. The rare earthoxide(s) source may contain, or only provide, rare earth oxide(s).Alternatively, the rare earth oxide(s) source may contain, or providerare earth oxide(s), as well as one or more metal oxides other than rareearth oxide(s) (including materials of or containing complex rare earthoxide.other metal oxides (e.g., Dy₃Al₅O₁₂, CeAl₁₁O₁₈, etc.)).

In some embodiments, it may be advantageous for at least a portion of ametal oxide source (in some embodiments, 10, 15, 20, 25, 30, 35, 40, 45,50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or even 100 percent by weight)to be obtained by adding particulate, metallic material comprising atleast one of a metal (e.g., Al, Ca, Cu, Cr, Fe, Li, Mg, Ni, Ag, Ti, Zr,and combinations thereof), M, that has a negative enthalpy of oxideformation or an alloy thereof to the melt, or otherwise combining themwith the other raw materials. Although not wanting to be bound bytheory, it is believed that the heat resulting from the exothermicreaction associated with the oxidation of the metal is beneficial in theformation of a homogeneous melt and resulting glass. For example, it isbelieved that the additional heat generated by the oxidation reactionwithin the raw material eliminates, minimizes, or at least reducesinsufficient heat transfer, and hence facilitates formation andhomogeneity of the melt, particularly when forming glass particles withx, y, and z dimensions over 50 (over 100, or even over 150) micrometers.It is also believed that the availability of the additional heat aids indriving various chemical reactions and physical processes (e.g.,densification, and spherodization) to completion. Further, it isbelieved for some embodiments, the presence of the additional heatgenerated by the oxidation reaction actually enables the formation of amelt, which otherwise is difficult or not practical due to high meltingpoint of the materials. Further, the presence of the additional heatgenerated by the oxidation reaction actually enables the formation ofglass that otherwise could not be made, or could not be made in thedesired size range. Another advantage of the invention includes, informing the glasses, that many of the chemical and physical processessuch as melting, densification and spherodizing can be achieved in ashort time, so that very high quench rates may be achieved. Foradditional details, see publication No. US 2003-0110709-A1, thedisclosure of which is incorporated herein by reference.

In one aspect of the invention, the raw materials are fed independentlyto form the molten mixture. In another aspect of the invention, certainraw materials are mixed together, while other raw materials are addedindependently into the molten mixture. In some embodiments, for example,the raw materials are combined or mixed together prior to melting. Theraw materials may be combined in any suitable and known manner to form asubstantially homogeneous mixture. These combining techniques includeball milling, mixing, tumbling and the like. The milling media in theball mill may be metal balls, ceramic balls and the like. The ceramicmilling media may be, for example, alumina, zirconia, silica, magnesiaand the like. The ball milling may occur dry, in an aqueous environment,or in a solvent-based (e.g., isopropyl alcohol) environment. If the rawmaterial batch contains metal powders, then it is generally desired touse a solvent during milling. This solvent may be any suitable materialwith the appropriate flash point and ability to disperse the rawmaterials. The milling time may be from a few minutes to a few days,generally between a few hours to 24 hours. In a wet or solvent basedmilling system, the liquid medium is removed, typically by drying, sothat the resulting mixture is typically homogeneous and substantiallydevoid of the water and/or solvent. If a solvent based milling system isused, during drying, a solvent recovery system may be employed torecycle the solvent. After drying, the resulting mixture may be in theform of a “dried cake”. This cake-like mixture may then be broken up orcrushed into the desired particle size prior to melting. Alternatively,for example, spray-drying techniques may be used. The latter typicallyprovides spherical particulates of a desired oxide mixture. Theprecursor material may also be prepared by wet chemical methodsincluding precipitation and sol-gel. Such methods will be beneficial ifextremely high levels of homogeneity are desired.

Particulate raw materials are typically selected to have particle sizessuch that the formation of a homogeneous melt can be achieved rapidly.Typically, raw materials with relatively small average particle sizesand narrow distributions are used for this purpose. In some methods(e.g., flame forming and plasma spraying), particularly desirableparticulate raw materials are those having an average particle size in arange from about 5 nm to about 50 micrometers (in some embodiments, in arange from about 10 nm to about 20 micrometers, or even about 15 nm toabout 1 micrometer), wherein at least 90 (in some embodiments, 95, oreven 100) percent by weight of the particulate is the raw material,although sizes outside of the sizes and ranges may also be useful.Particulate less than about 5 nm in size tends to be difficult to handle(e.g., the flow properties of the feed particles tended to beundesirable as they tend to have poor flow properties). Use ofparticulate larger than about 50 micrometers in typical flame forming orplasma spraying processes tend to make it more difficult to obtainhomogenous melts and glasses and/or the desired composition.

Furthermore, in some cases, for example, when particulate material isfed in to a flame or thermal or plasma spray apparatus to form the melt,it may be desirable for the particulate raw materials to be provided ina range of particle sizes. Although not wanting to be bound by theory,it is believed that this maximizes the packing density and strength ofthe feed particles. If the raw material powders are too coarse, the feedand resulting melt particles may not have the desired composition oruniformity. In general, the coarsest raw material particles should besmaller than the desired melt or glass particle sizes. Further, rawmaterial particles that are too coarse, tend to have insufficientthermal and mechanical stresses in the feed particles, for example,during a flame forming or plasma spraying step. The end result in suchcases is generally fracturing of the feed particles in to smallerfragments, loss of compositional uniformity, loss of yield in desiredglass particle sizes, or even incomplete melting as the fragmentsgenerally change their trajectories in a multitude of directions out ofthe heat source.

The glasses and ceramics comprising glass can be made, for example, byheating (including in a flame or plasma) the appropriate metal oxidesources to form a melt, (desirably a homogenous melt) and then coolingthe melt to provide glass. Some embodiments of glasses can be made, forexample, by melting the metal oxide sources in any suitable furnace(e.g., an inductively or resistively heated furnace, a gas-firedfurnace, or an electric arc furnace).

The glass is typically obtained by relatively rapidly cooling the moltenmaterial (i.e., the melt). The quench rate (i.e., the cooling time) toobtain the glass depends upon many factors, including the chemicalcomposition of the melt, the glass-forming ability of the components,the thermal properties of the melt and the resulting glass, theprocessing technique(s), the dimensions and mass of the resulting glass,and the cooling technique. In general, relatively higher quench ratesare required to form glasses comprising higher amounts of Al₂O₃ (i.e.,greater than 75 percent by weight Al₂O₃), especially in the absence ofknown glass formers such as SiO₂, B₂O₃, P₂O₅, GeO₂, TeO₂, As₂O₃, andV₂O₅. Similarly, it is more difficult to cool melts into glasses inlarger dimensions, as it is more difficult to remove heat fast enough.

In some embodiments of the invention, the raw materials are heated intoa molten state in a particulate form and subsequently cooled into glassparticles. Typically, the particles have a particle size greater than 25micrometers (in some embodiments, greater than 50, 100, 150, or even 200micrometers).

The quench rates achieved in making glasses according to the methods ofthe present invention are believed to be higher than 10², 10³, 10⁴, 10⁵or even 10⁶° C./sec (i.e., a temperature drop of 1000° C. from a moltenstate in less than 10 seconds, less than a second, less than a tenth ofa second, less than a hundredth of a second or even less than athousandth of a second, respectively). Techniques for cooling the meltinclude discharging the melt into a cooling media (e.g., high velocityair jets, liquids (e.g., cold water), metal plates (including chilledmetal plates), metal rolls (including chilled metal rolls), metal balls(including chilled metal balls), and the like). Other cooling techniquesknown in the art include roll-chilling. Roll-chilling can be carriedout, for example, by melting the metal oxide sources at a temperaturetypically 20-200° C. higher than the melting point, andcooling/quenching the melt by spraying it under high pressure (e.g.,using a gas such as air, argon, nitrogen or the like) onto a high-speedrotary roll(s). Typically, the rolls are made of metal and arewater-cooled. Metal book molds may also be useful for cooling/quenchingthe melt.

The cooling rate is believed to affect the properties of the quenchedglass. For instance, glass transition temperature, density and otherproperties of glass typically change with cooling rates.

Rapid cooling may also be conducted under controlled atmospheres, suchas a reducing, neutral, or oxidizing environment to maintain and/orinfluence the desired oxidation states, etc. during cooling. Theatmosphere can also influence glass formation by influencingcrystallization kinetics from undercooled liquid. For example, largerundercooling of Al₂O₃ melts without crystallization has been reported inargon atmosphere as compared to that in air.

In one method, glasses and ceramics comprising glass can be madeutilizing flame fusion as reported, for example, in U.S. Pat. No.6,254,981 (Castle). In this method, the metal oxide sources are fed(e.g., in the form of particles, sometimes referred to as “feedparticles”) directly into a burner (e.g., a methane-air burner, anacetylene-oxygen burner, a hydrogen-oxygen burner, and the like), andthen quenched, for example, in water, cooling oil, air, or the like. Thesize of feed particles fed into the flame generally determines the sizeof the resulting particles comprising glass.

Some embodiments of glasses can also be obtained by other techniques,such as: laser spin melting with free fall cooling, Taylor wiretechnique, plasmatron technique, hammer and anvil technique, centrifugalquenching, air gun splat cooling, single roller and twin rollerquenching, roller-plate quenching, and pendant drop melt extraction(see, e.g., Rapid Solidification of Ceramics, Brockway et al., MetalsAnd Ceramics Information Center, A Department of Defense InformationAnalysis Center, Columbus, Ohio, January, 1984). Some embodiments ofglasses may also be obtained by other techniques, such as: thermal(including flame or laser or plasma-assisted) pyrolysis of suitableprecursors, physical vapor synthesis (PVS) of metal precursors andmechanochemical processing.

Other techniques for forming melts, cooling/quenching melts, and/orotherwise forming glass include vapor phase quenching, plasma spraying,melt-extraction, and gas or centrifugal atomization. Vapor phasequenching can be carried out, for example, by sputtering, wherein themetal alloys or metal oxide sources are formed into a sputteringtarget(s). The target is fixed at a predetermined position in asputtering apparatus, and a substrate(s) to be coated is placed at aposition opposing the target(s). At typical pressures of 10⁻³ torr ofoxygen gas and Ar gas, a discharge is generated between the target(s)and substrate(s), and Ar or oxygen ions collide against the target tocause reaction sputtering, thereby depositing a film of composition onthe substrate. For additional details regarding plasma spraying, see,for example, publication No. US 2004-0023078-A1, the disclosure of whichis incorporated herein by reference.

Gas atomization involves heating feed particles to convert them to amelt. A thin stream of such melt is atomized through contact with adisruptive air jet (i.e., the stream is divided into fine droplets). Theresulting substantially discrete, generally ellipsoidal glass particles(e.g., beads) are then recovered. Examples of bead sizes include thosehaving a diameter in a range of about 5 micrometers to about 3 mm.Melt-extraction can be carried out, for example, as reported in U.S.Pat. No. 5,605,870 (Strom-Olsen et al.). Container-less glass formingtechniques utilizing laser beam heating as reported, for example, inU.S. Pat. No. 6,482,758 (Weber), may also be useful in making the glass.

Typically, glass-ceramics made according to the present invention, andsome glasses and ceramics comprising glasses used to make suchglass-ceramics, have x, y, and z dimensions each perpendicular to eachother, and wherein each of the x, y, and z dimensions are at least 10micrometers. In some embodiments, the x, y, and z dimensions are atleast 30 micrometers, 35 micrometers, 40 micrometers, 45 micrometers, 50micrometers, 75 micrometers, 100 micrometers, 150 micrometers, 200micrometers, 250 micrometers, 500 micrometers, 1000 micrometers, 2000micrometers, 2500 micrometers, 5 mm, or even at least 10 mm, ifcoalesced. The x, y, and z dimensions of a material are determinedeither visually or using microscopy, depending on the magnitude of thedimensions. The reported z dimension is, for example, the diameter of asphere, the thickness of a coating, or the shortest dimension of aprismatic shape.

The addition of certain other metal oxides may alter the propertiesand/or crystalline structure or microstructure of glass-ceramics madeaccording to the present invention, as well as the processing of the rawmaterials and intermediates in making the ceramic. For example, oxideadditions such as CaO, Li₂O, MgO, and Na₂O have been observed to alterboth the T_(g) and T_(x) (wherein T_(x) is the crystallizationtemperature) of glass. Although not wishing to be bound by theory, it isbelieved that such additions influence glass formation. Further, forexample, such oxide additions may decrease the melting temperature ofthe overall system (i.e., drive the system toward lower meltingeutectic), and ease glass formation. Compositions based upon complexeutectics in multi-component systems (quaternary, etc.) may have betterglass-forming ability. The viscosity of the liquid melt and viscosity ofthe glass in its' working range may also be affected by the addition ofmetal oxides other than the particular required oxide(s).

Crystallization of glasses and ceramics comprising the glass to formglass-ceramics may also be affected by the additions of materials. Forexample, certain metals, metal oxides (e.g., titanates and zirconates),and fluorides may act as nucleation agents resulting in beneficialheterogeneous nucleation of crystals. Also, addition of some oxides maychange the nature of metastable phases devitrifying from the glass uponreheating. In another aspect, for glass-ceramics made according to thepresent invention comprising crystalline ZrO₂, it may be desirable toadd metal oxides (e.g., Y₂O₃, TiO₂, CeO₂, CaO, and MgO) that are knownto stabilize the tetragonal/cubic form of ZrO₂.

The particular selection of metal oxide sources and other additives formaking glass-ceramics made according to the present invention typicallytakes into account, for example, the desired composition, themicrostructure, the degree of crystallinity, the physical properties(e.g., hardness or toughness), the presence of undesirable impurities,and the desired or required characteristics of the particular process(including equipment and any purification of the raw materials beforeand/or during fusion and/or solidification) being used to prepare theceramics.

In some instances, it may be preferred to incorporate limited amounts ofmetal oxides selected from the group consisting of: B₂O₃, Na₂O, P₂O₅,SiO₂, TeO₂, V₂O₅, and combinations thereof. Sources, includingcommercial sources, include the oxides themselves, complex oxides,elemental (e.g., Si) powders, ores, carbonates, acetates, nitrates,chlorides, hydroxides, etc. These metal oxides may be added, forexample, to modify a physical property of the resulting glass-ceramicand/or improve processing. These metal oxides, when used, are typicallyadded from greater than 0 to 20% by weight collectively (in someembodiments, greater than 0 to 5% by weight collectively, or evengreater than 0 to 2% by weight collectively) of the glass-ceramicdepending, for example, upon the desired property.

The microstructure or phase composition (glassy/crystalline) of amaterial can be determined in a number of ways. Various information canbe obtained using optical microscopy, electron microscopy, differentialthermal analysis (DTA), and x-ray diffraction (XRD), for example.

Using optical microscopy, amorphous material is typically predominantlytransparent due to the lack of light scattering centers such as crystalboundaries, while crystalline material shows a crystalline structure andis opaque due to light scattering effects.

A percent amorphous (or glass) yield can be calculated for particles(e.g., beads), etc. using a −100+120 mesh size fraction (i.e., thefraction collected between 150-micrometer opening size and125-micrometer opening size screens). The measurements are done in thefollowing manner. A single layer of particles, beads, etc. is spread outupon a glass slide. The particles, beads, etc. are observed using anoptical microscope. Using the crosshairs in the optical microscopeeyepiece as a guide, particles, beads, etc. that lay along a straightline are counted either amorphous or crystalline depending on theiroptical clarity (i.e., amorphous if they were clear). A total of 500particles, beads, etc. are typically counted, although fewer particles,beads, etc. may be used and a percent amorphous yield is determined bythe amount of amorphous particles, beads, etc. divided by totalparticles, beads, etc. counted. Embodiments of methods according to thepresent invention have percent amorphous (or glass) yields of at least50, 60, 70, 75, 80, 85, 90, 95, or even 100 percent.

If it is desired for all the particles to be amorphous (or glass), andthe resulting yield is less than 100%, the amorphous (or glass)particles may be separated from the non-amorphous (or non-glass)particles. Such separation may be done, for example, by any conventionaltechniques, including separating based upon density or optical clarity.

Using DTA, the material is classified as amorphous if the correspondingDTA trace of the material contains an exothermic crystallization event(T_(x)). If the same trace also contains an endothermic event (T_(g)) ata temperature lower than T_(x) it is considered to include a glassphase. If the DTA trace of the material contains no such events, it isconsidered to contain crystalline phases.

Differential thermal analysis (DTA) can be conducted using the followingmethod. DTA runs can be made (using an instrument such as that obtainedfrom Netzsch Instruments, Selb, Germany under the trade designation“NETZSCH STA 409 DTA/TGA”) using a −140+170 mesh size fraction (i.e.,the fraction collected between 105-micrometer opening size and90-micrometer opening size screens). An amount of each screened sample(typically about 400 milligrams (mg)) is placed in a 100-microliterAl₂O₃ sample holder. Each sample is heated in static air at a rate of10° C./minute from room temperature (about 25° C.) to 1100° C.

Using powder x-ray diffraction, XRD, (using an x-ray diffractometer suchas that obtained under the trade designation “PHILLIPS XRG 3100” fromPhillips, Mahwah, N.J., with copper K α1 radiation of 1.54050 Angstrom)the phases present in a material can be determined by comparing thepeaks present in the XRD trace of the crystallized material to XRDpatterns of crystalline phases provided in JCPDS (Joint Committee onPowder Diffraction Standards) databases, published by InternationalCenter for Diffraction Data. Furthermore, XRD can be used qualitativelyto determine types of phases. The presence of a broad diffuse intensitypeak is taken as an indication of the amorphous nature of a material.The existence of both a broad peak and well-defined peaks is taken as anindication of existence of crystalline matter within a glass matrix.

The initially formed glass or ceramic (including glass prior tocrystallization) may be larger in size than that desired. If the glassis in a desired geometric shape and/or size, size reduction is typicallynot needed. The glass or ceramic can be converted into smaller piecesusing crushing and/or comminuting techniques known in the art, includingroll crushing, jaw crushing, hammer milling, ball milling, jet milling,impact crushing, and the like. In some instances, it is desired to havetwo or multiple crushing steps. For example, after the ceramic is formed(solidified), it may be in the form of larger than desired. The firstcrushing step may involve crushing these relatively large masses or“chunks” to form smaller pieces. This crushing of these chunks may beaccomplished with a hammer mill, impact crusher or jaw crusher. Thesesmaller pieces may then be subsequently crushed to produce the desiredparticle size distribution. In order to produce the desired particlesize distribution (sometimes referred to as grit size or grade), it maybe necessary to perform multiple crushing steps. In general the crushingconditions are optimized to achieve the desired particle shape(s) andparticle size distribution. Resulting particles that are not of thedesired size may be re-crushed if they are too large, or “recycled” andused as a raw material for re-melting if they are too small.

The shape of particles can depend, for example, on the compositionand/or microstructure of the ceramic, the geometry in which it wascooled, and the manner in which the ceramic is crushed (i.e., thecrushing technique used). In general, where a “blocky” shape ispreferred, more energy may be employed to achieve this shape.Conversely, where a “sharp” shape is preferred, less energy may beemployed to achieve this shape. The crushing technique may also bechanged to achieve different desired shapes. For some particles anaverage aspect ratio ranging from 1:1 to 5:1 is typically desired, andin some embodiments, 1.25:1 to 3:1, or even 1.5:1 to 2.5:1.

It is also within the scope of the present invention, for example, todirectly form articles in desired shapes. For example, desired articlesmay be formed (including molded) by pouring or forming the melt into amold. Also see, for example, the forming techniques described inapplication having U.S. Ser. No. 10/358,772, filed Feb. 5, 2003, thedisclosure of which is incorporated herein by reference.

Embodiments of glasses and glass-ceramics made according to the presentinvention can be obtained without limitations in dimensions. This wasfound to be possible through a coalescing step performed at atemperature above the glass transition temperature. This coalescing stepin essence forms a larger sized body from two or more smaller particles.For instance, a glass undergoes glass transition (T_(g)) beforesignificant crystallization occurs (T_(x)) as evidenced by the existenceof an endotherm (T_(g)) at lower temperature than an exotherm (T_(x)).For example, ceramic (including glass prior to crystallization), mayalso be provided by heating, for example, particles comprising theglass, and/or fibers, etc. above the T_(g) such that the particles, etc.coalesce to form a shape. The temperature and pressure used forcoalescing may depend, for example, upon composition of the glass andthe desired density of the resulting material. The temperature should begreater than the glass transition temperature. In certain embodiments,the heating is conducted at at least one temperature in a range of about700° C. to about 1100° C. (in some embodiments, 725° C. to 850° C.).Typically, the glass is under pressure (e.g., greater than zero to 1 GPaor more) during coalescence to aid the coalescence of the glass. In oneembodiment, a charge of the particles, etc. is placed into a die andhot-pressing is performed at temperatures above glass transition whereviscous flow of glass leads to coalescence into a relatively large part.Examples of typical coalescing techniques include hot pressing, hotisostatic pressing, hot extrusion, hot forging and the like (e.g.,sintering, plasma assisted sintering). For example, particles comprisingglass (obtained, for example, by crushing) (including beads andmicrospheres), fibers, etc. may formed into a larger particle size.Coalescing may also result in a body shaped into a desired form. In someembodiments, it is desirable to cool the resulting coalesced body beforefurther heat treatment. After heat treatment if so desired, thecoalesced body may be crushed to smaller particle sizes or a desiredparticle size distribution.

In general, heat-treatment can be carried out in any of a variety ofways, including those known in the art for heat-treating glass toprovide glass-ceramics. For example, heat-treatment can be conducted inbatches, for example, using resistive, inductively or gas heatedfurnaces. Alternatively, for example, heat-treatment (or a portionthereof) can be conducted continuously, for example, using a rotarykiln, fluidized bed furnaces, or pendulum kiln. In the case of a rotarykiln or a pendulum kiln, the material is typically fed directly into thekiln operating at the elevated temperature. In the case of a fluidizedbed furnace, the glass to be heat-treated is typically suspended in agas (e.g., air, inert, or reducing gasses). The time at the elevatedtemperature may range from a few seconds (in some embodiments, even lessthan 5 seconds) to a few minutes to several hours. The temperaturetypically ranges from the T_(x) of the glass to 1600° C., more typicallyfrom 800° C. to 1600° C., and in some embodiments, from 1200° C. to1500° C. It is also within the scope of the present invention to performsome of the heat-treatment in multiple steps (e.g., one for nucleation,and another for crystal growth; wherein densification also typicallyoccurs during the crystal growth step). When a multiple stepheat-treatment is carried out, it is typically desired to control eitheror both the nucleation and the crystal growth rates. In general, duringmost ceramic processing operations, it is desired to obtain maximumdensification without significant crystal growth. Although not wantingto be bound by theory, in general, it is believed in the ceramic artthat larger crystal sizes lead to reduced mechanical properties whilefiner average crystallite sizes lead to improved mechanical properties(e.g., higher strength and higher hardness). In particular, it is verydesirable to form ceramics with densities of at least 90, 95, 97, 98,99, or even 100 percent of theoretical density, wherein the averagecrystal sizes are less than 0.15 micrometer, or even less than 0.1micrometer.

In some embodiments of the present invention, the glasses or ceramicscomprising glass may be annealed prior to heat-treatment. In such casesannealing is typically done at a temperature less than the T_(x) of theglass for a time from a few second to few hours or even days. Typically,the annealing is done for a period of less than 3 hours, or even lessthan an hour. Optionally, annealing may also be carried out inatmospheres other than air. Furthermore, different stages (i.e., thenucleation step and the crystal growth step) of the heat-treatment maybe carried out under different atmospheres. It is believed that theT_(g) and T_(x), as well as the T_(x)-T_(g) of the glasses may shiftdepending on the atmospheres used during the heat treatment.

One skilled in the art can determine the appropriate conditions from aTime-Temperature-Transformation (TTT) study of the glass usingtechniques known in the art. One skilled in the art, after reading thedisclosure of the present invention should be able to provide TTT curvesfor glasses used to make glass-ceramics according to the presentinvention, determine the appropriate nucleation and/or crystal growthconditions to provide glass-ceramics according to the present invention.

Heat-treatment may occur, for example, by feeding the material directlyinto a furnace at the elevated temperature. Alternatively, for example,the material may be fed into a furnace at a much lower temperature(e.g., room temperature) and then heated to desired temperature at apredetermined heating rate. It is within the scope of the presentinvention to conduct heat-treatment in an atmosphere other than air. Insome cases it might be even desirable to heat-treat in a reducingatmosphere(s). Also, for, example, it may be desirable to heat-treatunder gas pressure as in, for example, a hot-isostatic press, or in agas pressure furnace. Although not wanting to be bound by theory, it isbelieved that atmospheres may affect oxidation states of some of thecomponents of the glasses and glass-ceramics. Such variation inoxidation states can bring about varying coloration of glasses andglass-ceramics. In addition, nucleation and crystallization steps can beaffected by atmospheres (e.g., the atmosphere may affect the atomicmobilities of some species of the glasses).

It is also within the scope of the present invention to conductadditional heat-treatment to further improve desirable properties of thematerial. For example, hot-isostatic pressing may be conducted (e.g., attemperatures from about 800° C. to about 1400° C.) to remove residualporosity, increasing the density of the material. It is within the scopeof the present invention to convert (e.g., crush) the resulting articleor heat-treated article to provide particles (e.g., abrasive particles)made according to the present invention.

Typically, glass-ceramics are stronger than the glasses from which theyare formed. Hence, the strength of the material may be adjusted, forexample, by the degree to which the glass is converted to crystallineceramic phase(s). Alternatively, or in addition, the strength of thematerial may also be affected, for example, by the number of nucleationsites created, which may in turn be used to affect the number, and inturn the size of the crystals of the crystalline phase(s). Foradditional details regarding forming glass-ceramics, see, for example,Glass-Ceramics, P.W. McMillan, Academic Press, Inc., 2^(nd) edition,1979.

As compared to many other types of ceramic processing (e.g., sinteringof a calcined material to a dense, sintered ceramic material), there isrelatively little shrinkage (typically, less than 30 percent by volume;in some embodiments, less than 20 percent, 10 percent, 5 percent, oreven less than 3 percent by volume) during crystallization of the glassto form the glass-ceramic. The actual amount of shrinkage depends, forexample, on the composition of the glass, the heat-treatment time, theheat-treatment temperature, the heat-treatment pressure, the density ofthe glass being crystallized, the relative amount(s) of the crystallinephases formed, and the degree of crystallization. The amount ofshrinkage can be measured by conventional techniques known in the art,including by dilatometry, Archimedes method, or measuring the dimensionsof the material before and after heat-treatment. In some cases, theremay be some evolution of volatile species during heat-treatment.

In some embodiments, the relatively low shrinkage feature may beparticularly advantageous. For example, articles may be formed in theglass phase to the desired shapes and dimensions (i.e., in near-netshape), followed by heat treatment to at least partially crystallize theglass. As a result, substantial cost savings associated with themanufacturing and machining of the crystallized material may berealized.

In some embodiments, the glass has an x, y, z direction, each of whichhas a length of at least 1 cm (in some embodiments, at least 5 cm, oreven at least 10 cm), wherein the glass has a volume, wherein theresulting glass-ceramic has an x, y, z direction, each of which has alength of at least 1 cm (in some embodiments, at least 5 cm, or even atleast 10 cm), wherein the glass-ceramic has a volume of at least 70 (insome embodiments, at least 75, 80, 85, 90, 95, 96, or even at least 97)percent of the glass volume.

Examples of crystalline phases which may be present in glass-ceramicsmade according to the present invention include: alumina (e.g., alphaand transition aluminas), REO (e.g., La₂O₃), Y₂O₃, MgO, one or moreother metal oxides such as BaO, CaO, Cr₂O₃, CoO, Fe₂O₃, GeO₂, Li₂O, MnO,NiO, Na₂O, P₂O₅, Sc₂O₃, SiO₂, SrO, TeO₂, TiO₂, V₂O₅, ZnO, HfO₂, ZrO₂(e.g., cubic ZrO₂ and tetragonal ZrO₂), as well as “complex metaloxides” (including complex Al₂O₃.metal oxide (e.g., complex Al₂O₃.REO(e.g., ReAlO₃ (e.g., GdAlO₃, LaAlO₃), ReA₁₁O₁₈ (e.g., LaAl₁₁O₁₈), andRe₃Al₅O₁₂ (e.g., Dy₃Al₅O₁₂)), and complex Al₂O₃.Y₂O₃ (e.g., Y₃Al₅O₁₂)),complex ZrO₂.REO (e.g., La₂Zr₂O₇)), complex ZrO₂.Nb₂O₅, complexZrO₂.Ta₂O₅, complex Y₂O₃.Nb₂O₅, complex Y₂O₃.Ta₂O₅, complex Al₂O₃.Nb₂O₅,complex Al₂O₃.Ta₂O₅, and combinations thereof. Typically, ceramicsaccording to the present invention are free of eutectic microstructurefeatures.

It is also with in the scope of the present invention to substitute aportion of the aluminum cations in a complex Al₂O₃.metal oxide (e.g.,complex Al₂O₃.REO and/or complex Al₂O₃.Y₂O₃ (e.g., yttrium aluminateexhibiting a garnet crystal structure)) with other cations. For example,a portion of the Al cations in a complex Al₂O₃.Y₂O₃ may be substitutedwith at least one cation of an element selected from the groupconsisting of: Cr, Ti, Sc, Fe, Mg, Ca, Si, Co, and combinations thereof.For example, a portion of the Y cations in a complex Al₂O₃.Y₂O₃ may besubstituted with at least one cation of an element selected from thegroup consisting of: Ce, Dy, Er, Eu, Gd, Ho, La, Lu, Nd, Pr, Sm, Th, Tm,Yb, Fe, Ti, Mn, V, Cr, Co, Ni, Cu, Mg, Ca, Sr, and combinations thereof.Further, for example, a portion of the rare earth cations in a complexAl₂O₃.REO may be substituted with at least one cation of an elementselected from the group consisting of: Y, Fe, Ti, Mn, V, Cr, Co, Ni, Cu,Mg, Ca, Sr, and combinations thereof. The substitution of cations asdescribed above may affect the properties (e.g. hardness, toughness,strength, thermal conductivity, etc.) of the ceramic.

Crystals formed by heat-treating amorphous material to provideembodiments of glass-ceramics made according to the present inventionmay be, for example, acicular equiaxed, columnar, or flattenedsplat-like features.

Although the glass or glass-ceramic may be in the form of a bulkmaterial, it is also within the scope of the present invention toprovide composites comprising glass and/or glass-ceramic made accordingto the present invention. Such a composite may comprise, for example, aphase or fibers (continuous or discontinuous) or particles (includingwhiskers) (e.g., metal oxide particles, boride particles, carbideparticles, nitride particles, diamond particles, metallic particles,glass particles, and combinations thereof) dispersed in glass-ceramicmade according to the present invention, or a layered-compositestructure (e.g., a gradient of glass-ceramic to glass used to make theglass-ceramic and/or layers of different compositions ofglass-ceramics).

Certain glasses used to make the glass-ceramics may have, for example, aT_(g) in a range of about 700° C. to about 850° C., or even highertemperatures.

In some embodiments, the glass or glass-ceramic according to the presentinvention does not comprise (in some embodiments, does not consistessentially of) 35.73 (in some embodiments, about 35 or 36; in someembodiments, in a range from 35 to 36, 34 to 36, or 34 to 37) percent byweight Al₂O₃, 42.17 (in some embodiments, about 42; in some embodiments,in a range from 42 to 43 or 41 to 43) percent by weight Y₂O₃ (in someembodiments, Y₂O₃ and/or (including collectively) REO), 17.1 (in someembodiments, about 17; in some embodiments, in a range from 17 to 18 or16 to 18) percent by weight ZrO₂ (in some embodiments, ZrO₂ and/or(including collectively) HfO₂), and 5 (in some embodiments, about 5; insome embodiments, in a range from 4 to 6) percent by weight Nb₂O₅ and/or(including collectively) Ta₂O₅, based on the total weight of the glassor glass-ceramic, respectively.

In some embodiments of glasses and glass-ceramics according to thepresent invention, if the glass or glass-ceramic comprises Al₂O₃ (insome embodiments, 35.73 percent by weight Al₂O₃; in some embodiments,about 35 or 36 percent by weight Al₂O₃; in some embodiments, in a rangefrom 35 to 36, 34 to 36, or 34 to 37 percent by weight Al₂O₃), Y₂O₃ (insome embodiments, Y₂O₃ and/or (including collectively) REO) (in someembodiments, 42.17 percent by weight Y₂O₃ (in some embodiments, Y₂O₃and/or (including collectively) REO); in some embodiments, about 42percent by weight La₂O₃ (in some embodiments, Y₂O₃ and/or (includingcollectively) REO); in some embodiments, in a range from 42 to 43 or 41to 43) percent by weight La₂O₃ (in some embodiments, Y₂O₃ and/or(including collectively) REO), and ZrO₂ (in some embodiments, ZrO₂and/or (including collectively) HfO₂) (in some embodiments, 17.1 percentby weight ZrO₂ (in some embodiments, at least one of ZrO₂ or HfO₂); insome embodiments, about 17 percent by weight ZrO₂ (in some embodiments,at least one of ZrO₂ or HfO₂); in some embodiments, in a range from 17to 18 or 16 to 18) percent by weight ZrO₂ (in some embodiments, at leastone of ZrO₂ or HfO₂) are present, the glass or glass-ceramic compriseseither less than or greater than 5 (in some embodiments, not about 5,less than 5, or greater than 5; in some embodiments, not greater than 4,3, 2, or 1 or at least 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50,55, 60, 65, 70, 75, or even at least 80) percent by weight of the atleast one of Nb₂O₅ or Ta₂O₅, based on the total weight of the glass orglass-ceramic, respectively.

Typically, and desirably, the (true) density, sometimes referred to asspecific gravity, of glass-ceramics made according to the presentinvention, and glasses used to make such glass-ceramics, is typically atleast 70% of theoretical density. More desirably, the (true) density ofglass-ceramics made according to the present invention, and glasses usedto make such glass-ceramics is at least 75%, 80%, 85%, 90%, 95%, 96%,97%, 98%, 99%, 99.5%, or even 100% of theoretical density. Abrasiveparticles made according to the present invention have densities of atleast 85%, 90%, 92%, 95%, 96%, 97%, 98%, 99%, 99.5%, or even 100% oftheoretical density.

Articles can be made using glass-ceramics made according to the presentinvention, for example, as a filler, reinforcement material, and/ormatrix material. For example, glass-ceramic made according to thepresent invention can be in the form of particles and/or fibers suitablefor use as reinforcing materials in composites (e.g., ceramic, metal, orpolymeric (thermosetting or thermoplastic)). The particles and/or fibersmay, for example, increase the modulus, heat resistance, wearresistance, and/or strength of the matrix material. Although the size,shape, and amount of the particles and/or fibers used to make acomposite may depend, for example, on the particular matrix material anduse of the composite, the size of the reinforcing particles typicallyrange from about 0.1 to 1500 micrometers, more typically 1 to 500micrometers, and desirably between 2 to 100 micrometers. The amount ofparticles for polymeric applications is typically about 0.5 percent toabout 75 percent by weight, more typically about 1 to about 50 percentby weight. Examples of thermosetting polymers include: phenolic,melamine, urea formaldehyde, acrylate, epoxy, urethane polymers, and thelike. Examples of thermoplastic polymers include: nylon, polyethylene,polypropylene, polyurethane, polyester, polyamides, and the like.

Examples of uses for reinforced polymeric materials (i.e., reinforcingparticles made according to the present invention dispersed in apolymer) include protective coatings, for example, for concrete,furniture, floors, roadways, wood, wood-like materials, ceramics, andthe like, as well as, anti-skid coatings and injection molded plasticparts and components.

Further, for example, glass-ceramic made according to the presentinvention can be used as a matrix material. For example, glass-ceramicsmade according to the present invention can be used as a binder forceramic materials and the like such as diamond, cubic-BN, Al₂O₃, ZrO₂,Si₃N₄, and SiC. Examples of useful articles comprising such materialsinclude composite substrate coatings, cutting tool inserts abrasiveagglomerates, and bonded abrasive articles such as vitrified wheels. Theglass-ceramics made according to the present invention can be used asbinders, for example, to increase the modulus, heat resistance, wearresistance, and/or strength of the composite article.

Optical waveguides according to the present invention may be madegenerally by fabrication means known to one of ordinary skill in theart. For example, a channel waveguide (see FIG. 2) may be fabricated bydepositing a doped glass layer on a lowindex cladding, followed byphoto-lithography and etching to define a line. The lithography isusually followed by the deposition of a low index top cladding. A ridgewaveguide (see FIG. 3) is similar to a channel waveguide except that thedoped glass layer is not fully etched back. A strip-loaded waveguide(see FIG. 4) may be made by placing a strip of low-index cladding on aplanar layer of doped glass. A diffused waveguide (see FIG. 5) may bemade by indiffusing a doped glass into the low-index substrate. Thedoped glasses may be deposited onto a low index layer or cladding byknown methods in the art such as sputtering and followed byphotolithography to define lines or ridges. Alternatively, the dopedglasses may be deposited onto a low index layer or cladding by knownmethods in the art such as sputtering and then the doped glass layer maybe covered by a low index layer (see FIG. 6). Glass fibers using thedoped glasses described herein as the core of the fibers may befabricated by well known methods, such as reported in “Rare earth dopedfiber lasers and amplifiers”, Ed., M. J. F. Digonnet, 1993, MarcelDekker, Inc. and in U.S. Pat. No. 6,484,539 B1 (Nordine et al.) and U.S.Pat. No. 6,490,081 B1 (Feillens et al.).

Certain glass-ceramic particles made according to the present inventioncan be particularly useful as abrasive particles. The abrasive particlescan be incorporated into an abrasive article, or used in loose form.Abrasive particles made according to the present invention generallycomprise crystalline ceramic (e.g., at least 75, 80, 85, 90, 91, 92, 93,94, 95, 96, 97, 98, 99, 99.5, or even 100 percent by volume crystallineceramic). In another aspect, the present invention provides a pluralityof particles having a particle size distribution ranging from fine tocoarse, wherein at least a portion of the plurality of particles areabrasive particles made according to the present invention. In anotheraspect, embodiments of abrasive particles made according to the presentinvention generally comprise (e.g., at least 75, 80, 85, 90, 91, 92, 93,94, 95, 96, 97, 98, 99, 99.5, or even 100 percent by volume)glass-ceramic made according to the present invention.

Abrasive particles are usually graded to a given particle sizedistribution before use. Such distributions typically have a range ofparticle sizes, from coarse particles to fine particles. In the abrasiveart this range is sometimes referred to as a “coarse”, “control” and“fine” fractions. Abrasive particles graded according to industryaccepted grading standards specify the particle size distribution foreach nominal grade within numerical limits. Such industry acceptedgrading standards (i.e., specified nominal grades) include those knownas the American National Standards Institute, Inc. (ANSI) standards,Federation of European Producers of Abrasive Products (FEPA) standards,and Japanese Industrial Standard (JIS) standards. In one aspect, thepresent invention provides a plurality of abrasive particles having aspecified nominal grade, wherein at least a portion of the plurality ofabrasive particles are abrasive particles made according to the presentinvention. In some embodiments, at least 5, 10, 15, 20, 25, 30, 35, 40,45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or even 100 percent byweight of the plurality of abrasive particles are the abrasive particlesmade according to the present invention, based on the total weight ofthe plurality of abrasive particles.

In another aspect, the present invention provides an abrasive article(e.g., a bonded abrasive article, a non-woven abrasive article, or acoated abrasive article) comprising a binder and a plurality of abrasiveparticles, wherein at least a portion of the abrasive particles are theabrasive particles made according to the present invention.

In some embodiments, the present invention provides a method for makingabrasive particles, the method comprising heat-treating glass particlesto convert at least a portion of the glass to glass-ceramic and providethe abrasive particles. In some embodiments, the method furthercomprises grading the abrasive particles to provide a plurality ofparticles having a specified nominal grade. In some embodiments, themethod further comprises incorporating the abrasive particles into anabrasive article.

Abrasive articles comprise binder and a plurality of abrasive particles,wherein at least a portion of the abrasive particles are the abrasiveparticles made according to the present invention. Exemplary abrasiveproducts include coated abrasive articles, bonded abrasive articles(e.g., wheels), non-woven abrasive articles, and abrasive brushes.Coated abrasive articles typically comprise a backing having first andsecond, opposed major surfaces, and wherein the binder and the pluralityof abrasive particles form an abrasive layer on at least a portion ofthe first major surface.

In some embodiments, at least 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55,60, 65, 70, 75, 80, 85, 90, 95, or even 100 percent by weight of theabrasive particles in an abrasive article are the abrasive particlesmade according to the present invention, based on the total weight ofthe abrasive particles in the abrasive article.

Additional details regarding embodiments of ceramics (including methodsof making and using the same) comprising at least Al₂O₃, REO, and atleast one of Nb₂O₅ or Ta₂O₅ may be found, for example, in publicationNo. US 2005-0060948-A1, the disclosure of which is incorporated hereinby reference. Additional details regarding embodiments of ceramics(including methods of making and using the same) comprising at least twoof (a) Al₂O₃, (b) REO, or (c) at least one of ZrO₂ or HfO₂, and at leastone of Nb₂O₅ or Ta₂O₅ may be found, for example, in publication No. US2005-0065013-A1, the disclosure of which is incorporated herein byreference.

Advantages and embodiments of this invention are further illustrated bythe following non-limiting examples, but the particular materials andamounts thereof recited in these examples, as well as other conditionsand details, should not be construed to unduly limit this invention. Allparts and percentages are by weight unless otherwise indicated. Unlessotherwise stated, all examples contained no significant amount of SiO₂,B₂O₃, P₂O₅, GeO₂, TeO₂, As₂O₃, and V₂O₅.

EXAMPLES 1-14

A polyethylene bottle was charged with 100 grams of the componentslisted in Table 1 below. The sources of the raw materials used arelisted in Table 2, below. The Er₂₂O₃ source was Er(NO₃).5H₂O, and theamount used took into account an oxide yield of about 43 wt %. TABLE 1Wt. Wt. Glass % % Wt. % Wt. % Wt. % Wt. % Yield Example Y₂0₃ Al₂0₃ ZrO₂Nb₂O₅ Ta₂O₅ Er₂O₃ Vol. % 1 15.68 8.9 73.83 1.58 >95 2 39.26 5.94 53.271.52 >95 3 15.07 46.5 36.96 1.46 >95 4 10.53 5.98 82.48 0.99 >95 5 29.054.4 65.53 1 >95 6 12.12 37.42 49.44 1 >95 7 49.38 14.47 35.15 1 >60 855.24 12.18 31.58 1 >70 9 34.24 27.58 37.18 1 >95 10 9.87 11.92 77.191 >75 11 8.22 26.49 64.28 1 >85 12 27.41 22.08 49.49 1 >90 13 6.50 7.8684.59 1 >50 14 5.74 18.52 74.72 1 >75

TABLE 2 Raw Material Source Alumina (Al₂O₃) powder Obtained from CondeaVista, Tucson, AZ under the trade designation “APA-0.5” Erbium NitratePentahydrate Obtained from Aldrich Chemical, (ErNO₃•5H₂O) Milwaukee, WIYttrium Oxide (Y₂O₃) powder Obtained from Molycorp Inc., Mountain Pass,CA Tantalum Oxide (Ta₂O₅) powder Obtained from Aldrich Chemical NiobiumOxide (Nb₂O₅) powder Obtained from Aldrich Chemical Zirconium Oxide(ZrO₂) powder Obtained under the trade designation “DK-1” from ZirconiaSales, Inc. of Marietta, GA

For each example, about 400 grams of zirconia milling media (obtainedfrom Tosoh Ceramics, Division of Bound Brook, N.J. under the tradedesignation “YTZ”) were added to the bottle along with 100 ml distilledand deionized water. The mixture was milled for 24 hours at 120 rpm.After the milling, the milling media were removed and the slurry waspoured onto a glass (“PYREX”) pan where it was dried using a heat-gun.Before melting in a flame, dried particles were calcined at 1300° C. for1 hour in air in an electrically heated furnace (obtained under thetrade designation “Model KKSK-666-3100” from Keith Furnaces of PicoRivera, Calif.). After grinding with a mortar and pestle, a portion ofthe calcined particles were fed into a hydrogen/oxygen torch flame. Thehydrogen torch used to melt the multiphase particles, thereby generatinga melted glass bead, was a Bethlehem bench burner (PM2D Model B obtainedfrom Bethlehem Apparatus Co., Hellertown, Pa.). For the inner ring, thehydrogen flow rate was 8 standard liters per minute (SLPM), the oxygenflow rate was 3 SLPM. For the outer ring, the hydrogen flow rate was 23standard liters per minute (SLPM), the oxygen flow rate was 9.8 SLPM.The dried and sized particles were fed directly into the hydrogen torchflame, where they were melted and transported to an inclined stainlesssteel surface (approximately 20 inches wide with the slope angle of 45degrees) with cold water running over (approximately 81/min.).

The resulting molten and quenched particles were collected in a pan anddried at 110° C. The particles were spherical in shape and varied insize from a few tens of micrometers up to 250 micrometers.

A percent amorphous yield was calculated from the resulting flame-formedbeads using a −100+120 mesh size fraction (i.e., the fraction collectedbetween 150-micrometer opening size and 125-micrometer opening sizescreens). The measurements were done in the following manner. A singlelayer of beads was spread out upon a glass slide. The beads wereobserved using an optical microscope. Using the crosshairs in theoptical microscope eyepiece as a guide, beads that lay horizontallycoincident with the crosshair along a straight line were counted eitheramorphous or crystalline depending on their optical clarity (i.e., theywere amorphous if clear). A total of 500 beads were counted and apercent amorphous yield was determined by the amount of amorphous beadsdivided by total beads counted. The amorphous yield data for the flameformed beads of Examples 1-14 are reported in Table 1, above.

EXAMPLES 15 and 16

Portions of beads of Example 1 and 4 were heat-treated in a furnace (anelectrically heated furnace (obtained under the trade designation “ModelKKSK-666-3100” from Keith Furnaces of Pico Rivera, Calif.)) as followsto provide Examples 15 and 16, respectively. The beads were heated fromroom temperature (about 25° C.) to about 1300° C. at a rate of about 10°C./min. and then held at 1300° C. for about 1 hour. Next, the beads werecooled back to room temperature by turning off the furnace.

FIGS. 8 and 9 are scanning electron microscope (SEM) digitalphotomicrographs at 15,000X and 20,000X, respectively, of polishedsections of heat-treated Example 1 and 4 materials showing thecrystalline nature of the materials. The polished sections were preparedusing conventional mounting and polishing techniques. Polishing was doneusing a polisher (obtained from Buehler of Lake Bluff, Ill. under thetrade designation “ECOMET 3 TYPE POLISHER-GRINDER”). The samples werepolished for about 3 minutes with a diamond wheel containing125-micrometer diamonds, followed by three minutes of polishing witheach of 45, 30, 15, 9, and 3 micrometers diamond slurries. The polishedsamples were coated with a thin layer of gold—palladium and viewed usingJEOL SEM (Model JSM 840A).

Various modifications and alterations of this invention will becomeapparent to those skilled in the art without departing from the scopeand spirit of this invention, and it should be understood that thisinvention is not to be unduly limited to the illustrative embodimentsset forth herein.

1. Glass-ceramic collectively comprising at least 70 percent by weightof (i) at least one of Nb₂O₅ or Ta₂O₅ and (ii) at least two of (a)Al₂O₃, (b) Y₂O₃, or (c) at least one of ZrO₂ or HfO₂, and the glasscontaining not more than 30 percent by weight collectively As₂O₃, B₂O₃,GeO₂, P₂O₅, SiO₂, TeO₂, and V₂O₅, based on the total weight of theglass-ceramic.
 2. The glass-ceramic according to claim 1, wherein ifAl₂O₃, at least one of Y₂O₃ or REO, and at least one of ZrO₂ or HfO₂ arepresent, the glass-ceramic comprises either not greater than 4 or atleast 6 percent by weight of the at least one of Nb₂O₅ or Ta₂O₅, basedon the total weight of the glass-ceramic.
 3. The glass-ceramic accordingto claim 1, wherein if Al₂O₃, at least one of Y₂O₃ or REO, and at leastone of ZrO₂ or HfO₂ are present, the glass-ceramic comprises at least 6percent by weight of the at least one of Nb₂O₅ or Ta₂O₅, based on thetotal weight of the glass-ceramic.
 4. The glass-ceramic according toclaim 3 collectively comprising at least 75 percent by weight of (i) atleast one of Nb₂O₅ or Ta₂O₅ and (ii) at least two of (a) Al₂O₃, (b)Y₂O₃, or (c) at least one of ZrO₂ or HfO₂, based on the total weight ofthe glass-ceramic.
 5. The glass-ceramic according to claim 3collectively comprising at least 80 percent by weight of (i) at leastone of Nb₂O₅ or Ta₂O₅ and (ii) at least two of (a) Al₂O₃, (b) Y₂O₃, or(c) at least one of ZrO₂ or HfO₂, based on the total weight of theglass-ceramic.
 6. The glass-ceramic according to claim 3 collectivelycomprising at least 85 percent by weight (i) at least one of Nb₂O₅ orTa₂O₅ and (ii) at least two of (a) Al₂O₃, (b) Y₂O₃, or (c) at least oneof ZrO₂ or HfO₂, based on the total weight of the glass-ceramic.
 7. Theglass-ceramic according to claim 3 collectively comprising at least 90percent by weight of (i) at least one of Nb₂O₅ or Ta₂O₅ and (ii) atleast two of (a) Al₂O₃, (b) Y₂O₃, or (c) at least one of ZrO₂ or HfO₂,based on the total weight of the glass-5 ceramic.
 8. The glass-ceramicaccording to claim 3 collectively comprising at least 95 percent byweight of (i) at least one of Nb₂O₅ or Ta₂O₅ and (ii) at least two of(a) Al₂O₃, (b) Y₂O₃, or (c) at least one of ZrO₂ or HfO₂, based on thetotal weight of the glass-ceramic.
 9. The glass-ceramic according toclaim 3 collectively comprising at least 99 percent by weight of (i) atleast one of Nb₂O₅ or Ta₂O₅ and (ii) at least two of (a) Al₂O₃, (b)Y₂O₃, or (c) at least one of ZrO₂ or HfO₂, based on the total weight ofthe glass-ceramic.
 10. The glass-ceramic according to claim 3collectively comprising 100 percent by weight of (i) at least one ofNb₂O₅ or Ta₂O₅ and (ii) at least two of (a) Al₂O₃, (b) Y₂O₃, or (c) atleast one of ZrO₂ or HfO₂, based on the total weight of theglass-ceramic.
 11. The glass-ceramic according to claim 3 collectivelycomprising at least 70 percent by weight of Al₂O₃, at least one of ZrO₂or HfO₂, and at least one of Nb₂O₅ or Ta₂O₅, based on the total weightof the glass-ceramic.
 12. The glass-ceramic according to claim 11,wherein the at least one of ZrO₂ or HfO₂ is present in an amount of atleast 5 percent by weight, based on the total weight of theglass-ceramic.
 13. The glass-ceramic according to claim 11, wherein theat least one of ZrO₂ or HfO₂ is present in an amount of at least 10percent by weight, based on the total weight of the glass-ceramic. 14.The glass-ceramic according to claim 3 collectively comprising at least70 percent by weight of Al₂O₃, Y₂O₃, and at least one of Nb₂O₅ or Ta₂O₅,based on the total weight of the glass-ceramic.
 15. The glass-ceramicaccording to claim 14, wherein the at least one of Nb₂O₅ or Ta₂O₅ ispresent in an amount of at least 10 percent by weight, based on thetotal weight of the glass-ceramic.
 16. The glass-ceramic according toclaim 3 collectively comprising at least 70 percent by weight of Y₂O₃,at least one of ZrO₂ or HfO₂, and at least one of Nb₂O₅ or Ta₂O₅. 17.The glass-ceramic according to claim 16, wherein the at least one ofNb₂O₅ or Ta₂O₅ is present in an amount greater than 5 percent by weight,based on the total weight of the glass-ceramic.
 18. The glass-ceramicaccording to claim 16, wherein the at least one of Nb₂O₅ or Ta₂O₅ ispresent in an amount of at least 10 percent by weight, based on thetotal weight of the glass-ceramic.
 19. The glass-ceramic according toclaim 3 collectively comprising at least 70 percent by weight of Al₂O₃,Y₂O₃, at least one of ZrO₂ or HfO₂, and at least one of Nb₂O₅ or Ta₂O₅,based on the total weight of the glass-ceramic.
 20. The glass-ceramicaccording to claim 19, wherein the at least one of ZrO₂ or HfO₂ ispresent in an amount of at least 5 percent by weight, based on the totalweight of the glass-ceramic.
 21. The glass-ceramic according to claim19, wherein the at least one of ZrO₂ or HfO₂ is present in an amount ofat least 10 percent by weight, based on the total weight of theglass-ceramic.
 22. A method for making glass-ceramic according to claim3, the method comprising: heat-treating glass to convert at least aportion of the glass to crystalline ceramic and provide theglass-ceramic, the glass collectively comprising at least 70 percent byweight of (i) at least one of Nb₂O₅ or Ta₂O₅ and (ii) at least two of(a) Al₂O₃, (b) Y₂O₃, or (c) at least one of ZrO₂ or HfO₂, and the glasscontaining not more than 30 percent by weight collectively As₂O₃, B₂O₃,GeO₂, P₂O₅, SiO₂, TeO₂, and V₂O₅.
 23. A method for making glass-ceramicaccording to claim 3, the method comprising: heat-treating ceramiccomprising glass to convert at least a portion of the glass tocrystalline ceramic to provide the glass-ceramic, the glass collectivelycomprising at least 70 percent by weight of (i) at least one of Nb₂O₅ orTa₂O₅ and (ii) at least two of (a) Al₂O₃, (b) Y₂O₃, or (c) at least oneof ZrO₂ or HfO₂, and the glass containing not more than 30 percent byweight collectively As₂O₃, B₂O₃, GeO₂, P₂O₅, SiO₂, TeO₂, and V₂O₅. 24.The glass-ceramic according to claim 1 in the form of an IR window.